1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to an array substrate for a liquid crystal display device and a fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing a photocurrent generation and a signal delay in the liquid crystal display device.
2. Discussion of the Related Art
Flat panel display (FPD) devices having small size, lightweight, and low power consumption may have been a subject of recent research in the advent of the information age. Among many kinds of FPD devices, liquid crystal display (LCD) devices have been widely developed and used because of their excellent characteristics in resolution, color display, and display quality.
Generally, LCD devices include an upper substrate and a lower substrate facing into each other with liquid crystal molecules interposed therebetween. Each substrate has an electrode on the inner surface thereof. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images in accordance with the light transmittance.
The lower substrate is referred to as an array substrate including a thin film transistor (TFT) that is formed through repeated deposition of thin films, photolithography, and an etch process. The upper substrate is referred to as a color filter substrate including a color filter layer that is formed through a dyeing method, a printing method, a pigment dispersion method, or an electro-deposition method. Three colors of red (R), green (G), and blue (B) are alternately disposed in the color filter layer.
FIG. 1 is a cross-sectional view of a conventional LCD device.
In FIG. 1, a gate electrode 12 of a conductive material such as metal is formed on a first substrate 11. A gate insulating layer 13 of silicon nitride (SiNx) or silicon oxide (SiO2) is formed on the gate electrode 12. An active layer 14 of amorphous silicon is formed on the gate insulating layer 13 over the gate electrode 12. An ohmic contact layer 15a and 15b of doped amorphous silicon is formed on the active layer 14. Source and drain electrodes 16a and 16b of a conductive material such as metal are formed on the ohmic contact layer 15a and 15b. The source and drain electrodes 16a and 16b form a TFT “T” with the gate electrode 12. The gate electrode 12 and the source electrode 16a are connected to a gate line (not shown) and a data line (not shown), respectively. The gate line and the data line cross each other and define a pixel region. A passivation layer 17 of SiNx, SiO2, or an organic insulating material is formed on the source and drain electrodes 16a and 16b. The passivation layer 17 includes a contact hole 17c exposing the drain electrode 16b. A pixel electrode 18 of a transparent conductive material is formed on the passivation layer 17 and connected to the drain electrode 16b through the contact hole 17c. 
A second substrate 21 is disposed over and spaced apart from the first substrate 11. A black matrix 22 corresponding to the TFT “T” is formed beneath the second substrate 21. The black matrix 22 has an open portion (not shown) corresponding to the pixel electrode 18. The black matrix 22 prevents a light leakage at an LCD panel except for the pixel electrode 18 and a photocurrent generated by screening a channel of the TFT “T” from the ambient light. The black matrix 22 is formed in a color filter layer 23a and 23b. The color filter layer 23a and 23b having three colors of R, G, and B is alternately disposed. The color filter layer corresponds to the pixel region. A common electrode 24 of a transparent conductive material is formed beneath the color filter layer 23a and 23b. A liquid crystal layer 30 is interposed between the pixel electrode 18 and the common electrode 24.
The black matrix may prevent light from being leaked at an LCD panel except for the pixel electrode and photocurrent from being generated by screening a channel of the TFT from the ambient light. However, since the black matrix is spaced apart from the TFT, the black matrix does not shield the oblique incident light or a portion of the light reflected at the black matrix. Therefore, such light reaches the channel of the TFT, thereby generating a photocurrent. Moreover, the TFT becomes non-uniform in characteristics.
On the other hand, as LCD devices have larger size and higher resolution, a signal line becomes longer and narrower. Accordingly, a possibility of the signal delay increases. To reduce resistance of the signal line, a material of low resistivity such as aluminum (Al) or copper (Cu) is used for the signal line. Generally, a pixel electrode is formed of a transparent conductive material such as indium-tin-oxide (ITO). A contact resistance between ITO and Al is relatively high, and Cu is susceptible to an ITO etchant. Therefore, when Al or Cu is used for the signal line, an electrical short-circuit may occur at the contact portion between ITO and Al. Moreover, a signal may be distorted.